Damage Characterisation in Composite Laminates Using Vibro-Acoustic Technique

The need to characterise in-service damage in composite structures is increasingly becoming important as composites find higher utilisation in wind turbines, aerospace, automotive, marine, among others. This paper investigates the feasibility of simplifying the conventional acousto-ultrasonic technique set-up for quick and economic one-sided in-service inspection of composite structures. Acousto-ultrasonic technique refers to the approach of using ultrasonic transducer for local excitation while sensing the material response with an acoustic emission sensor. However, this involves transducers with several auxiliaries. The approach proposed herewith, referred to as vibro-acoustic testing, involves a low level of vibration impact excitation and acoustic emission sensing for damage characterisation. To test the robustness of this approach, first, a quasi-static test was carried out to impute low-velocity impact damage on three groups of test samples with different ply stacking sequences. Next, the vibro-acoustic testing was performed on all test samples with the acoustic emission response for the samples acquired. Using the acoustic emission test sample response for all groups, the stress wave factor was determined using the peak voltage stress wave factor method. The stress wave factor results showed an inverse correlation between the level of impact damage and stress wave factor across all the test sample groups. This corresponds with what has been reported in literature for acousto-ultrasonic technique; thus demonstrating the robustness of the proposed vibro-acoustic set-up. Structural health monitoring, impact damage, acousto-ultrasonic testing, non-destructive testing.

Multi-Resolution Analysis of the Acousto-Ultrasonic Testing Signal for Composite Material Detection

The AU technique is employed in this paper to test the specimen which is made up of composite shell and adiabatic layer; the noise in the tested signal is reduced by adaptive filtering; Multi-resolution analysis of the signal is achieved by wavelet transform. By comparing the ratio of the energy of signal in different frequency zones to the total energy, the characteristic frequency zone of the signal is gained. The characteristic frequency zone of the signal from specimen is evaluated by energy integral Stress Wave Factor (SWF). Flaws are found effectively, and the size of flaw can be evaluated qualitatively. The validity of AU test for bond quality of the structure is approved in the experiments.